# Synergistic energy harvesting and catalysis in B2SSe–MSSe (M = Mo, W) van der Waals heterostructures

## TL;DR

This paper explores how B2SSe–MSSe heterostructures can efficiently harvest energy and catalyze reactions under visible light.

## Contribution

The study introduces new Janus-based van der Waals heterostructures with promising optoelectronic and photocatalytic properties.

## Key findings

- B2SSe–MSSe heterostructures show type-II band alignment and strong visible light absorption.
- These materials enable efficient charge separation and spontaneous water splitting under visible light.
- They are promising for optoelectronic and hydrogen production applications.

## Abstract

In this study, we employed density functional theory (DFT) to investigate the structural, electronic, optical and photocatalytic properties of B2SSe–MSSe (M = Mo, W) van der Waals heterostructures (vdWHs). Due to the presence of different chalcogen atoms on either side of these Janus monolayers, multiple possible stacking patterns of B2SSe–MSSe heterostructures were constructed and analyzed. Their mechanical, thermal, and dynamical stabilities are confirmed via binding energies, Born criteria, ab initio molecular dynamics (AIMD) simulations, and phonon spectrum calculations. The weighted electronic band-structure analysis via both PBE and HSE06 functionals confirmed a type-II band alignment with an indirect bandgap. The intrinsic asymmetry of Janus materials introduces out-of-plane polarization and vertical electric fields, which facilitate efficient charge-carrier separation and migration, suppress recombination, and enhance photo-oxidation and visible-light absorption. Electrostatic potential profiles, charge density differences, and Bader charge analysis confirm interlayer charge transfer from the MSSe to the B2SSe monolayer, indicating p-type doping in the MSSe and n-type doping in the B2SSe of B2SSe–MSSe vdWHs. Higher carrier mobility in specific cases, verified via effective mass calculations, further promotes efficient charge transfer to the surface and reduces recombination across the interface of B2SSe–WSSe vdWHs, making them promising for light-detection and -harvesting applications. The imaginary part of dielectric function (ε2(ω)) indicating strong visible light absorption capacity. The valence and conduction band edge potentials were calculated to assess their photocatalytic suitability. The results demonstrate that B2SSe–MSSe vdWHs exhibit suitable band edges for overall water splitting at pH = 0, with the valence and conduction band edges straddling the redox potential window, enabling spontaneous oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) under visible light irradiation. These findings underscore the potential of the B2SSe–MSSe (M = Mo, W) vdWHs for optoelectronic and photocatalytic hydrogen production applications and offer a valuable framework for designing the next-generation optoelectronic and photoharvesting devices.

In this study, we employed density functional theory (DFT) to investigate the structural, electronic, optical and photocatalytic properties of B2SSe–MSSe (M = Mo, W) van der Waals heterostructures (vdWHs).